It has been increasingly suggested that some cases of rheumatoid arthritis (RA) and allied diseases may arise from the development of immunopathological responses following established or latent infection with a possible wide range of microorganisms. An extension of this view is that the different clinical syndromes within this group of disorders arise from immunoregulatory defects, the expression of which could be influenced by both genetic and environmental factors. Recent work in experimental animals regarding susceptibility to infectious agents strongly suggest that this is entirely possible. Furthermore, there are known rheumatic diseases of man for which there is now cogent evidence that infection and genetic influence play a role. Despite many attempts to identify the inciting infectious agent(s)in RA, results to date seem to be a negative catalogue of technical artifact and interpretative error. Careful examination of experimental protocols used in these studies coupled with recent conceptual and technical advances in microbiology, immunology and molecular biology provide plausible explanations of past failure. All indications are that the time has come to initiate another search. In general, previous investigations of RA have suffered from ill-defined parameters for disease classification and lack of interdisciplinary cooperation. The early stages of synovitis, which may provide valuable clues to pathogenesis, have received little study. The purpose of the present proposal is to define those infectious agents associated with rheumatoid arthritis of recent onset (2 to 12 mos.) in well characterized patient populations. The ability to detect organisms within affected joints will be enhanced by evaluation of synovial fluid and by evaluation of synovial tissue collected by arthroscopy. Current evidence suggests that two of the most likely agents to be involved in chronic arthritis in humans are mycoplasmas and chlamydiae. Thus, the present study will focus on these two organisms. Improved methods will be used for isolation of mycoplasmas and chlamydiae from synovial fluid and tissue, peripheral blood monocytes, and when indicated mucosal surfaces. Isolates will be identified using polyclonal and monoclonal antibodies. In addition, presence of microorganisms will be detected by amplication of nucleic acid by the highly sensitive and specific polymerase chain reaction (PCR). PCR will also be used to confirm species identity of mycoplasmal and chlamydial isolates. Detection of microorganisms directly in affected joints will be verified using immunoelectron microscopy and in situ hybridization. Detection of specific antibody to any organism detected in affected joints will be determined using enzyme-linked immunosorbent assays in conjunction with immunoblotting. Patient MHC genotypes will also be determined. Demographic and experimental data will be collected in such a way that all parameters may be correlated one with the other. All data obtained in RA will be compared to matched controls with osteoarthritis. We propose to accomplish these objectives by combining the investigative talents of individuals with backgrounds in clinical rheumatology, microbiology, molecular biology, immunology, genetics, epidemiology, and computer technology.